This Network proposes to carry out five specific aims to localize and characterize the genetic determinant of high BP. Aim 1 will use robust sibling pair linkage methods in 500 hypertensive sibling pairs in each racial group (a total of 1500 sibling pairs) to localize genes influencing interindividual differences in the occurrence of EHYT. Aims 2 and 3 will take advantage of previously collected BP and intermediate predictor trait data rom 1488 sibling pairs from the Rochester (MN) Family Heart Study to localize genes contributing to BP and EHYT. The proposed linkage analyses (Aims 1-3) will use both an extensive array of candidate genes and a large number of anonymous markers throughout the genome. Aim 4 will use multiple diallelic sequence polymorphisms and cladistic analyses within a linked gene to identify haplotypes for further DNA sequencing in order to identify candidate functional DNA sequence variation contributing to interindividual differences in BP level and EHYT status. Aim 5 will evaluate the ability of candidate functional DNA sequence variation to predict EHYT status in the three racial groups.